The present invention relates to seals for liquid level sight gages, and in particular, relates to a multi-part device fabricated of dissimilar materials to prevent leakage of the liquid.
The prior art abounds with different methods for mounting sight gages within connecting devices attached to a tank or reservoir which contains the water to be heated. Since the primary purpose of the sight gage is to indicate to the viewer the level of the water in the tank, it generally contains water and steam under pressure therein. The sight gage is generally located in close proximity to the boiler and comprises essentially a thick-walled transparent tube, which may be either glass or plastic, the upper end of which is connected to that portion of the boiler which is permanently in the vapor state and the lower end is connected to that portion of the boiler which always contains water. The sight gage itself is located at a level corresponding to that at which the water level of the boiler should be kept for satisfactory operation. It is the usual practice to provide valves to the upper, or steam connecting means, and the lower, or water connecting means. These valves are usually open at all times.
Criteria for such gages are well settled and will not be discussed herein. It will be clear to those skilled in the art that due to the high pressures and temperatures involved in steam boilers it is desirable to have a tight seal between the sight gage and the means connecting the gage to the boiler system. The seal generally utilized includes a rubber gasket and is compressed into place by the sealing nut. Unfortunately, it has been found in practice that under operating conditions it is virtually impossible to maintain an absolutely leak-proof seal due to the degregation of the gasket material. It is clearly impractical to replace the gasket as soon as it begins to deteriorate and it is impossible to maintain an adequate seal for a substantial period of time.
During operation, steam and water leak past the seal giving rise to three disadvantages. The first is the obscuring of the line of vision during the taking of the reading, another is the erosion of the surface of the sight gage and thirdly is the deposition thereon of previously dissolved solvent material. It has been found that unless these deposits are either prevented or immediately removed they will eventually cloud up the entire visibility of the glass. Corrosion is very hard on sight gages which utilize a transparent glass tube. This corrosion is caused by alkylinity and temperature. Most corrosion (thinning) on tubular glasses is above the water line at the upper half thereof. Here steam condenses and continually flows down the glass, eroding it. Boiler water with a pH of 11.5, for example, attacks glass 30 times faster than water with a pH of 8.5. The rate of attack from temperature increases 100 times from 265.degree. to 500.degree. F. When it is remembered that these sight gages are generally located at a height of about 14 feet about ground level in very close proximity of boilers operating at about 400.degree. F. it will be realized that keeping these sight gages clean is no simple or safe proposition. The nature of this problem, of course, has been known for many years. Many attempts have been made to provide an approved seal between the sight gage and the associated connecting device.
The prior art discloses different methods and devices which attempted to solve this basic problem. In particular, U.S. Pat. No. 630,047 issued to Gilbert on Aug. 1, 1899, discloses a one-piece rubber gasket having a centrally disposed protrusion. The gasket is adapted to fit over the sight gage glass and be frictionally held thereupon. Centrally disposed on the gasket is the protruding circumferential flange portion. One end of the sight glass, with the gasket thereon, is inserted into the cooperating tube. A compression nut having an enlarged opening is fit over the open end of the sight glass and is threaded onto the tube with a shoulder portion of the nut coming into contact with the lower portion of the gasket protrusion. Thus, as the nut is tightened on the tube the gasket is compressed against the circumference of the tube glass holding it in position.
U.S. Pat. No. 833,784 issued to Hicks on Oct. 23, 1907, attempts to solve the same problem by utilizing a metal ring which is provided on its outer edge with a downwardly depending flange, thus, forming an annular recess into which is inserted a packing-ring of rubber or similar material which is circular in cross-section. The upper portion of the ring is provided with a groove into which is inserted a number of balls. The balls are retained within this groove or raceway by a second smaller washer placed thereabove and held in position by a upperly-projecting flange provided on the ring and is adapted to be rolled over a smaller ring holding it in position. Thus, the assembled gland formed permits a compression nut to be freely rotated, allowing the rubber gasket material to compress against the outer circumference of a tubular sight gage when installed. The only area in intimate contact with the sight gage is the compressed rubber material.
U.S. Pat. No. 1,324,046 issued Dec. 9, 1919, to Hatfield attempts to solve the same problem in a slightly different manner. Therein, the sight glass is cut or etched proximate the ends thereof to form a series of grooves equally spaced and circumferentially disposed. The compression nut compresses the packing into the grooves and along the outer peripheral edges thereby attempting to seal the sight gage glass to the cooperating fitting.
U.S. Pat. No. 3,886,796 issued to Gruett on June 3, 1975, discloses a more conventional sealing mechanism which includes a pair of O-rings in intimate contact with the inner diameter of the sight gage as well as the outer edge.
All of the above sealing devices have been found satisfactory for short periods of time. However, each of these devices tends to deteriorate rather rapidly, thus requiring replacement of the sight gage in order to maintain an accurate reading.
Therefore, it is an object of the present invention to provide a means for maintaining the clarity of the sight gage by providing a more permanent type of seal. It is another object of the present invention to provide a device which is inexpensive and readily seals the sight gage with a connecting means.
It is a further object of the present invention to provide a gasket for glands which may be used with boilers operating at temperatures in the vicinity of 500.degree. F.
It is yet another object of the present invention to provide a gland which may last indefinitely and is ideally suited to the expansion and contraction characteristics of the sight gage.